Spectrographic pin stand



- March 23, 1948. E. J. DUNN SPECTROGRAPHIC PIN STAND Filed Feb. 12, 1947 6 Sheets-Sheet 1 90 &

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\ 3nventor dwam J Dam? His Gttorneg 6 Sheets-Sheet 2 E. J. 'DUNN SPECTROGRAPHIC PIN STAND Filed Feb. 12, 1947 fits (Ittomeg Z m M v 5 x w March 23, 1948.

E. J. DUNN- SPECTROGRAPHIC PIN STAND Filed Feb. 12, 1947 -6 Sheets-Sheet 5 3nventor rm (Ittorneg March 23, 1948. E. .1. DUNN SPECTROGRAPHIC PIN STAND 6 Sheets-Sheet 4 Filed Feb. 12, 1947 Jig. 7.

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I Enventor J. Dun/7 Edward H25 Gttorneg March 23, 1948. E. J. DUNN- SPECTROGRAPHJIZC PIN sum) Filed Feb. 12, 1947 6 Sheets-Sheet 5 Edward J Dun/7 Hls Gttomeg March 23, 1948.

E. J. DUNN SPECTQOGRAPHIC PIN STAND Filed b; 12, 1947 6 Sheets-Sheet 6 Edwa/a J Dun 7 1 (11s (Ittorneg Patented Mar. 23, 1948 SPEUTROGRTAPHIFC "PIN 7 S TZAND'" Edwasrd Ji DimmW'est Mifllim. 2a.,m5ssiimm1 w Carn eg-ie-Illinuisi Steel; Coriunratitm;.Ja..-corpora tion of New Jersey:

This invention relates to animproved standfbr' holding specimens for 'spectrographio analysis.

Among the objects of the inventionis-tl'ieprm vision of an improved spectrograp'hic' specimen stand, hereafter cal-led a spectrographic pin stand, which is adapted to be used for holding therein opposed pins or'one fiat sample-and'an opposed pin; the change from the first type of specimen to the second, or vice versa; hein'gnuiclely and easily accomplished.

A further object of the invention" lies in the provision-of-such spectrographic pin stand where= in the specimens consisting of the opposed 'pins or the opposed flat sampleand pin areeasilYand accurately located during loading.

Another object'ofthe' invention lies=in the provision of safety mechanism in combinationwit-h the hight'ension current supply'forsuchsp'ectrm graphic pin stand, whereby'fiow' o'fsuch current to the stand is prevented unless-the pin carrying slide is fully inse'rtedinto exciting positiona These and further objectsof the invention will be more readily apparent in the following descrip tion of a preferred embodiment of the invention.

Spectrographic analysis of materials is bein'g employed more and more Widelyboth in labora-- tory andproduction work since improvements'of the spectrographic equipment have-'made it' possibl'e todetermi'ne quantitatively cert'ain'elements with much greater speed than wet chemical methods and with comparable accuracy; This increased speed of analysismateriallyshor-tensthe time necessary for preparing certain-metals 'such as copper, aluminum, steel, iron; etc; and their alloys;

In general, there are two formsofspecim'ens which are employed in spectrographic analysis, the elongated'eleotrode or'pin andthefl'at plate. Thepin' may be made by casting the m'etalldesired to beanalyzed in pin form; The pin m'a-ry, however, consist of'a carloon electrodehaving 'aroavity iii-its end, the metal to be analyzedibein'gi' placed in such cavity in powdered form.. Theielectrodes are usually placed in a: pin stand on an optical bench of a spectrograph, thespecimenpinb'eingv placed on the bottom in avertical position and a plain'carbon electrode being placed iniopposed relationship with a standard gap between them. The application of astandard voltage-tethe elem trodes forms an arc betweenthem, theispectrum of which is analyzed by the spectrograph;

Heretofore, flat samples of; metals tol be: 311215- lyze'd'have been heldin' astand"calledlthePetrey stand; which is of quite different design: from that of: the pin holders. previously 'used. I'm the Sucliope'ration' required a' oonsiderab'le amount of 2. Peti'ey stanWthe flat sample isheldin horiiontal position above" a vertical carbon electrode placed at a standard distance from the underside thereof? tli'e a'ro' then bei-h'g created between the upper-end:- ofthe electrode and' tiie' lower-surface oftheflat- -sample. Formerly;when=it was= neoes mete change from the analysis; of" pins to flat sampi'eearrd vieeversaitwrrasnecessar t'complete 131 to remove one type of specimen holder from the: optical bench and: replace. it with another.

time. The in hoiderof the present? invention males possitile theclriange fromone typeoi sanr-r ple to another witlf only the removal of-aslidabl'e specimen or m holder from the stand and its replacement I By another" specimenholding" slide, an: operation which takes but a* few' seconds; Excitation' of the samp'les is revented byanovei safety mechanismnf the-invention until the speoiimen carrying slide inserted" in the'holder and lies in its op'e'ra-tive position:

The-" invention will bemore readily understood by reference to the accompanying-i drawings in which:

Figure 7 1* a View in elevationof the pin=stand a'ssembiy' with a holder" for two opposed pin sann ples-mounted tliereim Figure" 2 is a View planof theapparatus shown in-Figure l Figure 3 is a view in vertical section throug hthe pin: stand holder with the pin" holding s1ide*re moved} the section: being taken: alongthe line III-.-III of-Figur'efZ; I

Figure i i's an en'larged view in sideelevation of thepimholding'i slide- ShUWli-ifi Figures 1 and Eigure 5' isea view in horizontal cross: section through. the: ins holding" slide: of: Figure the view"beineitakenialongrthe;1ine;V--V= crfcE'igu-zfevti;

Figure fi-ii's-auview.inside elevationiofiaipinlpdsi 1 tionihgi jigr: employed: in the loading: of the: pin

hoidinezslideashown mil-Figures; l; 2H4; and; 5:1

Figure: 7: is: a View in; end; elevation"- of: theijig shown intv Figure 61 with; the" pin holding; slide shown: in: Figures; 4 9.1142115 mounted-1 therein; 4:

Figure=8iisiatview in sideelevation of the specimen. holder! with: a modified pin: holdinga slide placedithereinafnrrholdingr the-bottom: piniini the analysiaof flatrsamples;

Figurewis'a View in side "elevationofi'th'eibots tom: pin: holding slide: shown iin Figurez 8i;

Figure: 10 is atviewin. plan on the pini holding slideshowminrEigurezQ;

Figure: 1a; iszaz view imsiderelevation: of; ai'jig' for positioningztherpin; during; the: loading; of theislide shown 'inrmgurestaand 10;;

Figure 12 is a view in end elevation of the lie shown in Figure 11 with the pin holding slide shown in Figures 9 and mounted therein; and

Figure 13 is a diagrammatic view of the current supply and safety circuits for spectrographic pin stand.

The pin stand of the invention, indicated generally by the character 4 in Figure 1', is adapted for mounting upon the optical bench 2 of a spectrograph. The pin stand is provided with base 6 with the tracks of the bench. BaseB is provided with the central vertically projecting boss 8, and" with bosses I0 and I2 at the right and left hand: ends thereof, as shown in Figure 1, respectively.

The supporting frame for the specimen carrying slide is generally indicated by the reference character l4. Frame I4 is supported from the base 6 by means of Column I5, made of suitable insulating material such as a phenolic resin, ad- :iustably mounted, as shown, in boss 8; Frame 14- consists of a horizontal bottom plate I8 made of'metal having a longitudinal slot therein for {the reception of the lower edge of the pin holding slide, as shown in Figure 3. The frame is further provided with a metal top plate 26 parallel to plate I8, having a slot 28 therein extending throughout a major portion of the length of the plate. Plates I8 and 26 are connected by vertical insulating blocks, those at the left hand {side in Figure l at the front and back of the apparatus being designated 22 and 24, respectively. The-inner faces of the blocks are-placed in-alignment with the corresponding edgesofgslots fil and 28 to provide a'slide receiving'channel therebetween.. vBlock 22 is provided -with horizontal s1ot 25-t0 provide clearance for the-bottom pin retaining spring mounted on the pin holding slide, subsequently to be described.

The frame is completed by an insulating block 2'! shown at the right in Figure-1, having a-vertical slot in-its inner face lining up with slots 26 and 28. Top plate 26 of the frameis DIOvided with semi-circular recess 30 in the forward-portion thereof adjacent the slide receiving slot 28 and witha longitudinal opening 32 communicat- ;The body portion of such slide has a Vertically extending handle 38 made of an 'insulatingma- ,terial such as a phenolic resin, secured to the left hand edge'thereof as shown. The top electrode :or pin 40 and the bottom electrode or pin 42 are positioned in opposed coaxial relationship with :a predetermined standard gap between.

The slide is composed of top and bottom metal electrode carrying portions secured together to form a unitary structure in-which the two pin carrying portions are insulated from. each other. The top metal body portion 44, which is of a generally inverted U -shape as shown in Figure 4, is

provided centrally thereof with a vertical forward facing V groove v45 which receives the pin F40. The pin is held in the groove by a horizontalbent leaf spring 48. The bottom metal portion of the slide is likewiseprovided'withra vertical forward facing V groove 52 for the receptioniof bottom pin t2, the pin being retained in :the

having longitudinal grooves therein interfitting. 1'.

groove by the bent leaf spring 54. The two metal portions of the slide are connected at their forward ends by the insulating member 56, which may be made of synthetic resin. The upper and lower ends of member 56 extend into vertical slots in members 44 and 50, respectively, and are secured therein by bolts as shown. The rear ends of members 44 and 50 are connected together by being bolted to the integral handle 38 as shown in Figure 4. 7

To insure the correct initial setting of the top and bottom pins with the standard gap between their opposed ends there is provided the jig 86 2 shown in Figures 6 and 7. This jig is composed of a fiat plate 88 having generally the same length and height as the body of the slide. Plate 88 is provided with top and bottom flange plates 94 and 80, respectively, extending at right angles to plate88 and secured thereto as by screws. Plate 88 is further provided on one edge with a flange plate 95. The distance between the inner faces of plates 90 and 94 is made the same as the height 7 T-shaped member having oppositely extending feet I00 and the horizontal forwardly projecting gauge plate 98. slot provided in the face of plate 88 and are held therein by screws I04. Slots I02 in feet I00 7 through which screws I04 extend allow the verti- Whenthe slide is inserted in the frame the outer ,ends of the contacts extend within the V groove cal adjustment of gauge plate 98. r

. When slide 34 is inserted in the jig 86, as shown in Figure 7, pins 40 and 42 may be inserted in the grooves therein and thrust into engagement with gauge plate 98, the thickness of which is equal to the standard gap employed betweenthe electrodes in spectrographic analysis,

The supply of exciting voltag to pins 48 and Y42 is effected in the following manner. A conducton'not shown, connected to one side of a suitable current source extends through an insulator 80 carried by boss I2 and is connected to a binding post 64 from which connection to the bottom metal plate I8 of the pin stand frame is made by a jumper 68. A conductor connected to the other side of the current source is brought up through an insulator 58 carried by boss III to a binding post 62; from which connection is made to the upper plate 26 of theholder frame by a jumper 66. The upper metal portion of the pin carrying slide has spring pressed contacts. I6 adapted to engage plate 28, recessed into the rear face thereof as shown in Figure 4.

12 in plate 26, shown in Figure 3. Contact betweenthe lower metal portion 500i the pin carrying slide and plate I8 is efiected by'similar contacts 14, the ends of which extend within V groove in plate I8 when the slide is inserted in the channel in the holder.

In order to prevent connection of the holder to the high voltage source until the pin carry-e ing slide is inserted in the frame and is in'exciting position, I provide a safety mechanism shown .in Figures 1 and 2 and diagrammatically indicated in the circuit shown in Figure 13. Such mechanism consists of a microswitch 18 which makes and breaks a control circuit having leads '80 "and The construction of theswitch which is conventlo'nal is such thatits contacts Feet I00 fit within a-vertical caes um *are "normally openbut areclosed by engagement er the "slide with switch-actuating arm 84. A "-headed-pIunger BZ extends through a hole in the block '21,'"as shown, so that when the pin carryingslide 36-iswithdrawn, the innerend of plunger 82 may enter the slide receiving slot as arm 84 *is moved-byits=restoring spring to break thecircuit. Whenthe slideenters the slot, however, the forwar'd end-thereof engages the inherent! of plunger B'Z thrusting it outwardly, thereby actuatingarm "84 and closing the circuit.

"The manner in whichthe safety mechanism is connected to the current supply circuit will be moreclearly understood from Figure '13. Con- "ductor fifl leading to the holding means for pin 4 2, is connecteddirectly to one side of the source or high voltage, not shown. -A conductor I46 connected "to the otherside'of thesource, how- -ever,=is controlled by a manualswitch ltii and the contacts l'5il of a relay l48 controlled by the microswitch. 'The control circuit is provided with 'a =source of direct current I56, the microswitch being connected in series with such source and with the coil I52 of relay M8 by conductors 80, -8B'--and I58. The relay opens its contacts I50 when its coil is deenergized, thus breaking the high voltage circuit to the pin holder. When microswitch'lii is closed coil 152 is energized and contacts we in the supp-1y circuit are closed, "thereby putting the supply circuit in readiness for-arcing of the pins by the closing of the switch IBD.

When the specimen to be analyzed is 'a flat plate-the pin stand arrangement shownin Fig- =ures 8, 9, and 10 is employed. Such stand employs the same holder-as that used in the first embodiment; and the parts of holder and frame aredesignated by the same reference characters. "'For'arcing specimens of this type the slide 33 is replaced 'by'the slide tilt, shown in Figures 9 and 10,-for' holding the bottom plain carbon pin H 8. Slide 1'66 consists of a body ma, the insulatinghandle H0 being secured to the outer edge thereof, as shown in Figure 9. The body 'is'madeup of the bottom metal portion ll2'having the vertical forward facing v groove H4 thereinfor the reception of the lower portion of 'p'in ll'8,-the pin being secured in such groove by thebent leaf spring H6. The top portion of the slide-is made up of'the metal member I26, such 'partbeing secured to the lower member H2 at its forward end through the medium of insulatingmerriber [22, the ends of which fit in slots "in members IZOand I I2, respectively, and by han- =dle'-1 l0"towhich itis secured by bolts, as shown. Upper member I is provided with a forward facing recess I2 5 of substantial size as shown in Figure 10 'to give room for the are, such recess "communicating with an opening I26 extending throughthe rear face of member I20. Connection of member IE2 to the bottom plate i8 of the holder is effected by contacts I28 received in groove Hi, the top member l'2il being similarly :connected'to top metal plate 26 by contacts I30 :received in groove 12.

When the pin holding slide shown in Figures 9 :and 10 is inserted in the holder as shown in -Figure 8 the fiat metal specimen, not shown, is laid above the upper end of pin H8 and across the top frame member 25 and the top slide member l-'20,the upper surfaces of which lie in the same plane. The holder thereupon being supplied with exciting current, an-arc is struck between theupper end of the pin and the bottom surface or the fiat specimen.

'electro'de carrying "members "on the slide.

Correct "positioning of pin "11 8 is insured by "the use of jig r32 'shown in Figures 11 and 12. "Such jig is 'compose'd of ---'a main body-p1ate 134 having upper *and lower' 'fiange plates [-36 and 13B -'securedthereto. The jig is "also-provided "with 'aflange 1 40 on one edge. Friction plugs 'M'Z recessed in thebOttomplate F38 removably "retain slide Hit in the jigin-the position "shown in Figure 1 2. The upperfiange-plate 1361s provi'ded "on its 'lower edge with a gauge plat M4 *so'positione'd that it"will beengaged'bythe upper end of pin H8. The thickness 'of the gauge'plate is such that whenthe slide I 06 is inserted in the holder there will be-"a standard gapbetweenthe upper 'end of pin H8 and the bottomsurface -of "the flat sample-lying on'members' 26 and PM.

"A further'safetyfeature provided'in thedevice is an auxiliary gap'connected in *parallel'with the 'Such "auxiliary-"gap in" the first embodiment-consists of opposed members 1'62 afiixed to=parts44 and "50,

respectively, o'f'the-slide, and in the second 'embodim'ent consists of "opposed members 162' aifixed to parts H2 and 420, respectively, of 'the slide. The distance between'the adjacent *ends of members E2 and 162' is made-somewhat greater than the standard gap between electrodes or ,electro'dean'd fiat'sample sothat the arc occurs 'atthe sampleswhemtheyare in place and the holder energized. If the electrodes or electrode and flat "sample should "not be in position when the holder is'energized'however, the arc occurs "atlthe auxiliary gap, preventing the possibility of breakdown of thevarious insulating parts of the holder and's'lide.

Although I have illustrated and described a preferred embodiment of 'the improved spectrographic'pin stand of'my inveritionjthe latter is capable of considerable variation "within the teaching'of the invention. I, therefore, desire to claim as new the'following:

1. A spectrographic pin stand comprising a holder adapted to be mounted on an optical bench, said holder comprising a vertical frame having a vertical guideway extending substantially therethrough,the frame being made up of a 'lower horizontal electrically conducting member, an upper horizontal electrically conducting -member parallel thereto, and'laterally and longitudinal'ly spaced vertical electrically insulating members connecting'the'upper andlower conducting members, the lateral spacing of the "vertical members being sufiic-ient to form the More mentioned guideway, an electrode carrying slide 'adapte'dtobe snugly received in theguideway of 'theframe, means 'on the'sli'de to mount an e'lec trode in positionfor excitation and means on'the slide comprising a resiliently mounted contact making electrical connection 7 between one of the electrically conducting :members of the :frame 'ing the upper and lower members, the lateral spacing of the vertical membersbein'g such as to form a guideway of appreciable widththerebetween, the longitudinal spacing of thevertical members'being substantial-seasto form "an opening 20f appreciable siz transversely through the re earse frame, an electrode carrying slide adapted to be snugly' received in the guideway of'the frame, means on the slideto mount an electrode in position in front of the transverse opening through the frame thereon for excitation, a source of V conducting member, an upper horizontal electrically conducting member parallel thereto, and laterally and longitudinally spaced vertical electrically insulating members connecting the upper and lower members, the longitudinal spacing of the vertical members being substantial so as to form an opening of appreciable size transversely through the frame, the lateral spacing of the vertical members being such as to form the abovementioned guideway therebetween, an electrode carrying slide adapted to be snugly received in the guideway of the frame, means on the slide to mount an electrode in positionthereon for excitation, a source of exciting current, a circuit for connecting the two conducting members to opposite polarities of said source, means comprising a resiliently mounted contact making electrical connections between one of the electrically conducting'membersof the frame and the mounting means for the electrode, and means to open the exciting circuitwhen the slide is withdrawn appreciably from the exciting position in the guideway and to restore such circuit to a condition to be closed when the slide is advanced into exciting position in the guideway.

4. A spectrographic pin stand comprising a holder adapted to be mounted on an optical bench, said holder comprising a vertical frame, the frame being made up of a lower horizontal electrically conducting member, an upper horizontal electrically conducting member parallel thereto, and laterally and longitudinally spaced vertical electrically insulating members connecting the upper and lower members, the lateral spacing ofthe vertical members being such as to form a guideway of appreciable width therebe tween, the longitudinal spacing of the vertical members being substantial so as to form an opening of appreciable size transversely through the frame, an electrode carrying slide adapted to be snugly received in the guideway of the frame, means on the slide to mount an electrode in position thereon for excitation, a source of exciting current, a circuit for connecting the two con' ducting members to opposite polarities of. said source, means on the slide comprising a resiliently mounted contact making electrical connection between one of the electrically conducting meme bers of the frame and the mounting, means for when the coil is deenergized, in the first-mentioned circuit, means cpening and'closing the switch including a member operatively connected thereto and projecting into the guideway in position to be contacted by the slide when it is in exciting position to close the switch, v r

5. A spectrographic pin stand comprising a holder adapted to be mounted on an optical bench, said holder comprising a frame having a guideway therein, spaced electrically conducting members insulated from each other exposed in said guideway, a source of exciting current, means connecting the two conducting members to opposite polarities of said source, a removable electrode carrying slide adapted to be received in the guideway of the frame, two opposed mounting means on the slide electrically insulated from each other to mount opposed electrodes in position for excitation, means on the slide makingelectrical connection between one of the electrically conducting members of the frame and the mounting means for one of the electrodes,'and" means on the slide making electrical connection between the other of the electrically conducting members of the frame and the mounting means for the other of the electrodes. 7

6. A spectrcgraphic pin stand comprising a holder adapted to be mounted on an optical bench, said holder comprising a vertical frame having a vertical guideway extending substantially therethrough, the frame being made up of a lower horizontal electrically conducting member, an upper horizontal electrically conducting tion, means comprising a resiliently mounted contact making electrical connection between one-of the electrically conducting members of the frame and the mounting means for one of the electrodes,

4 and means comprising a resiliently mounted con-' tact making electrical connection between the other of the electrically conducting membersof the frame and the mounting means for the other of the pin samples. I

7. A spectrographic' pin stand comprising a I holder adapted to be mounted on an optical bench, said holder comprising a vertical'fraihe,

the frame being made up of a lower horizontal electrically conducting member, an'upper horizontal electrically conducting member parallel thereto, and laterally and longitudinally spaced vertical electrically insulating members connecting the upper and lower members, the lateral spacing of the vertical members being such as to form a guideway of appreciable width, therebe tween, the longitudinal spacing of the vertical the electrode, and means to open the exciting circuit when the slide is withdrawn appreciably from the exciting position in the guideway and to restore such circuit to a condition to be'closed members bein' substantial so as to form.v an

opening of appreciable size transversely through of the transverse opening through the frame, said means comprising an'electrode holdingmeanson the upper member of the slide and an opposed electrode holding means on the lower member of the slide, a source of exciting current, means connecting the two conducting members of the frame to opposite polarities of said source, and means making electrical connection between the upper conducting members of the frame and the slide and between the lower conducting members of the frame and the slide.

8. A spectrographic pin stand comprising a holder adapted to be mounted on an optical bench, said holder comprising a vertical frame, the frame being made up of a lower horizontal electrically conducting member, an upper horizontal electrically conducting member parallel thereto, and laterally and longitudinally spaced vertical electrically insulating members connecting the upper and lower members, the lateral spacing of the vertical members being such as to form a guideway of appreciable width therebetween, the longitudinal spacing of the vertical members being substantial so as to form an opening of appreciable size transversely through the frame, an electrode carying slide adapted to be snugly received in the guideway of the frame, said slide comprising spaced upper and lower members of electrically conducting material, insulating members connecting the upper and lower members, means on the slide to mount a pair of opposed electrodes in exciting position in front of the transverse opening through the frame, said means comprising an electrode holding means on the upper member of the slide and an opposed electrode holding means on the lower member of the slide, a source of exciting current, means connecting the two conducting members of the frame to opposite polarities of said source, and means to open the exciting circuit when the slide is withdrawn appreciably from the exciting position in the guideway and to restore such circuit to a condition to be closed when the slide is advanced into exciting position in the guideway.

9. A spectrographic pin stand for fiat samples comprising a holder adapted to be mounted on an optical bench, said holder comprising a Vertical frame having a guideway therein, upper and lower spaced electrically conducting members insulated from each other exposed in said guideway, the upper conducting member forming the top of the frame, a source of exciting current, means connecting the two conducting members to opposite polarities of said source, a removable electrode carrying slide adapted to be received in the guideway of the frame, means on the lower portion of the slide to mount an electrode in upright position for excitation, and means making electrical connection between the lower electrically conducting member of the frame and the mounting means for the electrode, the upper conducting member of the frame having a vertical opening therethrough in line with the electrode when the slide is inserted into the guideway in exciting position, whereby an arc may be struck between the electrode and the bottom surface of a fiat sample lying on the upper conducting member of the frame over the vertical opening therethrough.

10. A spectrographic pin stand for flat samples comprising a holder adapted to be mounted on an optical bench, said holder comprising a vertical frame having a vertical g-uideway extending substantially therethrough, the frame being made up of a lower horizontal electrically conducting member, an upper horizontal electrically conducting member parallel thereto, and laterally and longitudinally spaced vertical electrically insulating members connecting the upper and lower members, the lateral spacing of the vertical members being suflicient to form the aforementioned guideway, the longitudinal spacing of the vertical members being such as to form a transverse opening of substantial size through the frame, an electrode carrying slide adapted to be snugly received in the guideway of the frame, ;means on the lower portion of the slide to mount an electrode in upright position in front of the transverse opening for excitation, means comprising a resiliently mounted contact making electrical connection between the lower electrically conducting member of the frame and the mounting means on the slide for the electrode, the upper conducting member of the frame having a vertical opening therethrough in line with the electrode when the slide is inserted into the guideway in exciting position, whereby an arc may be struck between the electrode and the bottom surface of a flat sample lying on the upper conducting member of the frame over the vertical opening therethrough, and means to open the exciting circuit when the slide is withdrawn appreciably from the exciting position in the guideway and to restore such circuit to a condition to be closed when the slide is advanced into exciting position in the guideway.

EDWARD J. DUNN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,077,398 Douglas Nov. 4, 1913 2,282,643 Cutting May 12, 1942 2,344,719 Nusbaum Mar. 21, 1944 2,374,497 Pophal Apr. 24, 1945 Certificate of Correction Patent No. 2,438,158. March 23, 1948.

EDWARD J. DUNN It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 62, after the word between and before the period, insert their adjacent ends; column 5, line 37, after of insert the; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of May, A. D. 1948.

[nu-I THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents. 

